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G?i/o-coupled receptor signaling restricts pancreatic ?-cell expansion.

ABSTRACT: Gi-GPCRs, G protein-coupled receptors that signal via G? proteins of the i/o class (G?i/o), acutely regulate cellular behaviors widely in mammalian tissues, but their impact on the development and growth of these tissues is less clear. For example, Gi-GPCRs acutely regulate insulin release from pancreatic ? cells, and variants in genes encoding several Gi-GPCRs--including the ?-2a adrenergic receptor, ADRA2A--increase the risk of type 2 diabetes mellitus. However, type 2 diabetes also is associated with reduced total ?-cell mass, and the role of Gi-GPCRs in establishing ?-cell mass is unknown. Therefore, we asked whether Gi-GPCR signaling regulates ?-cell mass. Here we show that Gi-GPCRs limit the proliferation of the insulin-producing pancreatic ? cells and especially their expansion during the critical perinatal period. Increased Gi-GPCR activity in perinatal ? cells decreased ?-cell proliferation, reduced adult ?-cell mass, and impaired glucose homeostasis. In contrast, Gi-GPCR inhibition enhanced perinatal ?-cell proliferation, increased adult ?-cell mass, and improved glucose homeostasis. Transcriptome analysis detected the expression of multiple Gi-GPCRs in developing and adult ? cells, and gene-deletion experiments identified ADRA2A as a key Gi-GPCR regulator of ?-cell replication. These studies link Gi-GPCR signaling to ?-cell mass and diabetes risk and identify it as a potential target for therapies to protect and increase ?-cell mass in patients with diabetes.

SUBMITTER: Berger M

PROVIDER: S-EPMC4352814 | biostudies-other | 2015 Mar

REPOSITORIES: biostudies-other

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Gαi/o-coupled receptor signaling restricts pancreatic β-cell expansion.

Berger Miles M Scheel David W DW Macias Hector H Miyatsuka Takeshi T Kim Hail H Hoang Phuong P Ku Greg M GM Honig Gerard G Liou Angela A Tang Yunshuo Y Regard Jean B JB Sharifnia Panid P Yu Lisa L Wang Juehu J Coughlin Shaun R SR Conklin Bruce R BR Deneris Evan S ES Tecott Laurence H LH German Michael S MS

Proceedings of the National Academy of Sciences of the United States of America 20150218 9

Gi-GPCRs, G protein-coupled receptors that signal via Gα proteins of the i/o class (Gαi/o), acutely regulate cellular behaviors widely in mammalian tissues, but their impact on the development and growth of these tissues is less clear. For example, Gi-GPCRs acutely regulate insulin release from pancreatic β cells, and variants in genes encoding several Gi-GPCRs--including the α-2a adrenergic receptor, ADRA2A--increase the risk of type 2 diabetes mellitus. However, type 2 diabetes also is associa ...[more]

PMID: 25695968

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Project description:BACKGROUND:Lymphotoxin β receptor (LTβR) plays important roles in the development of the immune system and immune response. At the cellular level, ligand-bound LTβR activates the pro-inflammatory NF-κB pathway but the detailed mechanisms regulating its signaling remain unknown. Understanding them is of high importance since LTβR and its ligands are promising therapeutic targets. Here, we studied the consequences of perturbed cellular cholesterol content on LTβR-induced NF-κB signaling. METHODS:To modulate cholesterol availability and/or level in lung carcinoma A549 and H2228, and endothelial HUVEC cells different treatment regimens with filipin, methyl-β-cyclodextrin and simvastatin were applied. LTβR localization was studied by confocal microscopy. The activity of LTβR-induced NF-κB pathway was assessed by measuring the levels of NF-κB pathway inhibitor IκBα and phosphorylation of RelA transcription factor by Western blotting. The NF-κB transcriptional response, production of chemokines and adhesion molecules were examined by qRT-PCR, ELISA, and Western blotting, respectively. Adherence of different types of primary immune cells to epithelial A549 cells and endothelial HUVECs was measured fluorometrically. Interactions of LTβR with its protein partners were investigated by immunoprecipitation. RESULTS:We showed that filipin-mediated sequestration of cholesterol or its depletion from the plasma membrane with methyl-β-cyclodextrin impaired LTβR internalization and potentiated LTβR-dependent activation of the canonical branch of the NF-κB pathway. The latter was manifested by enhanced degradation of IκBα inhibitor, elevated RelA phosphorylation, substantial increase in the expression of NF-κB target genes encoding, among others, cytokines and adhesion molecules known to play important roles in immune response. It was followed by robust secretion of CXCL8 and upregulation of ICAM1, that favored the adhesion of immune cells (NK and T cells, neutrophils) to A549 cells and HUVECs. Mechanistically, we showed that cholesterol depletion stabilized interactions of ligand-stimulated LTβR with modified forms of TRAF2 and NEMO proteins. CONCLUSIONS:Our results showed that the reduction of the plasma membrane content of cholesterol or its sequestration strongly potentiated signaling outcome initiated by LTβR. Thus, drugs modulating cholesterol levels could potentially improve efficacy of LTβR-based therapies. Video abstract.

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G?i/o-coupled receptor signaling restricts pancreatic ?-cell expansion.

Publications

Gαi/o-coupled receptor signaling restricts pancreatic β-cell expansion.

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